Method for making polyimide microlithographic compositions soluble in alkaline media

ABSTRACT

Nonamic acidic functionalized diamines and dianhydrides are condensed to produce abnormal acid functionalized polyamic acid/imide resins which surprisingly afford effective lift-off, by alkaline media, even after higher imidization.

BACKGROUND OF THE INVENTION

The present invention generally relates to new and improved polyamicacid/imide microlithographic compositions, their method of manufacture,and particularly their use in a novel concurrent wet-development andimproved lift-off process.

Photoresist compositions are commonly used in microlithographicprocessing and generally consist of a diazoquinone photosensitizer and anovolak resin binder. Normally, such compositions are coated ontosemi-conductor substrates; and, when exposed to light of the properwavelength, they are chemically altered in their solubility to alkalinedeveloper solutions. Positive-working photoresists are initiallyinsolbule in the alkaline developer, but after exposure to light, theexposed regions will dissolve or "wet-develop" in alkaline solutionforming indented, micro-size line features. Subsequently, for manyapplications, the undissolved portion of the resist must be strippedfrom the substrate.

Positive-working novolak photoresists, however, are being increasinglyused under conditions which render them insoluble in conventionalstrippers. Ion implantation, plasma hardening, deep UV hardening andother high temperature processing conditions produce, for example,crosslinking reactions within the resist. This makes stripperpenetration and resist dissolution, which are essential to removal ofthe resists, virtually impossible.

Oxidative strippers such as hot sulfuric acid-hydrogen peroxide mixturescan be effective against intractable resists, but removal is often slowor incomplete. Moreover, these treatments are restricted to use onunmetallized substrates. Alternatively, removal of intractable resistsis sometimes possible by soaking in hot chlorinated and/or phenolicsolvents. However, toxicity and disposal problems associated with thesematerials are critical drawbacks to their use.

In the past there have been attempts to remove, otherwise intractable,photoresist compositions from metallized substrates with safe strippersolvents, devoid of the prior art problems. For example, IBM's U.S. Pat.No. 3,873,361 taught that novlak photoresist hardbaked at 210 degreescentigrade could be stripped with the conventional stripper solventN-methyl pyrrollidone. Although this liftoff process was specificallydesigned to accommodate the formation and removal of metallic maskinglayers above the resist, in practice, it simply failed to work becausethe N-methyl pyrollidone did not dissolve the hardened photoresist.

subsequently, IBM and others developed special solvent-soluble, liftoff(release) layers which were sandwiched between the substrate and eitherglass FIGS. 1 and 2), the photoresist (FIG. 3), or the metal mask (FIG.4). Disclosures of such release layer technology may be found in thefollowing list of prior art publications.

L. J. Fried, J. Havas, J. S. Lechaton, J. S. Logan, G. Paal and P. A.Totta, IBM J. Res. Develop., 26(3), 362 (1982).

B. J. Lin in Introduction to Microlithography; Theory, Materials andProcessing; ACS Symposium Seris Vol. 219, L. F. Thompson, C. G. Willson,and M. J. Bowne, Eds.; American Chemical Society (Washington); p. 287,1983.

J. Moran and D. Maydan, J. Va. Sci. Technol., 16(6), 1620 (1979).

D. M. Tennant, J. Vac. Sci. Technol., B1(2), 494 (1983)

J. A. Underhill, V. C. Nguyen, M. Kerbaugh, and D. Sundling i Advancesin Resist Technology and Processing II (1985); SPIE vol. 539; Society ofPhoto-Optical Instrumentaiton Engineers (Bellingham); p. 83, 1985.

P. Grabbe, E. L. Hu, and R. E. Howard, J. Vac. Sci. Technol, 21(1), 33(1982).

K. G. Sachdev, R. W. Kwong, M. R. Gupta, J. S. Chece, and J. S. Sachdev,U.S. Pat. No. 4,692,205 to IBM Corporation (1987). H. A. Protschka(IBM), European Patent Application 0 257 255 (1987).

One such solvent-soluble release layer material is polysulfone. Thismaterial has the advantage of enabling the liftoff of metal mask layerby conventional solvent stripping. Although the material also serves toinsulate and protect the metal substrate from attack by harsh oxidativestrippers, it all the same requires such harsh strippers to liftoff thephotoresist layer if hardened. Polysulfone can serve to liftoff thephotoresist material itself as in the fifth step of FIG. 3, but notwithout other drawbacks.

Such polysulfone release layers are insoluble to conventional alkalinedeveloping solutions. Accordingly, unlike the photoresist they are not"wet-developable". Patterns in the release layer must be made by"dry-development" with, for example, reactive ion etching. In fact,little if any commercial use has been made of these special releaselayers, in large part because they must be dry-developed.

In conventional microlithography, micron feature sizes developed by dryetching are excessively more expensive than wet etching. Additionally,the dry developable release layer material requires separate plasmaetching equipment in addition to that required to etch the photoresistlayer and other layers of multilayer microlithographic processing. Theaddition of even more equipment and more steps becomes such a seriousdrawback that those in the art have preferred the toxicity, disposal,and other restrictions associated with employing non-conventionalstrippers, to remove the photoresist layers, rather than deal with adry-developable release layers. Some otherwise acceptable release layermaterials do not adhere sufficiently to semi-conductor substrates or areincompatible surfaces for applying resist layers, or other organic orinorganic layers, thereto.

Accordingly, a wet-developable release layer of material that could beco-developed concurrently with the photoresist material, withoutrequiring separate plasma etching equipment, and which could be liftedoff by immersion in more mild and less toxic solvents and which wouldnot erode metallized substrates, while providing good adhesion tosemiconductor substrates and a compatable surface for applying resistlayers, or other organic or inorganic layers, would be a surprisingadvancement in the art fulfilling a long felt need in the industry.

SUMMARY OF THE INVENTION

It is therefore a principle object of the present invention to provide anew and improved wet-developable, release layer composition formultilayer microlithography which permits, otherwise insoluble,photoresist layers to e lifted off by mild, non-toxic, conventionalstrippers.

It is another principle object of the present invention to provide apolyamic acid/imide release layer which remains soluble in alkalinemedia even after substantial thermal imidization.

It is a further object of the present invention to provide a new andimproved method for making wet-developable release layers in multilayermicrolithography concurrently wet-developable with the positive-workingphotoresist.

It is an additional object of the present invention to provide a new andimproved microlithographic process for concurrently wed-developing aphotoresist layer along with its release layer and lifting off thephotoresist with conventional strippers whereby the need fordry-developed release agents, separate plasma processing equipment, andother additional steps and/or expense is negated.

It is also an object of this invention to provide a new and improvedmaterial for liftoff of overlying, nonimaged film.

These objects and other others are generally fulfilled by a new andimproved polyamic acid (ester)/imide polymer composition with regularlyinterposed nonamic acidic-functional moieties along the polymer backbonewhich are abnormal to the amic acid structure. These compositions may beemployed as a release layer, sandwiched between a semiconductorsubstrate and a photoresist layer, concurrently wet-developed with thephotoresist, thermally baked, and yet remain soluble in alkaline mediafor ease of liftoff.

The attached drawings, the following description of the drawings, thedetailed description of the preferred embodiments, and the examples willmore fully explain and illustrate the invention.

DESCRIPTION OF THE DRAWINGS

FIGS. 1 thru 4 illustrate four alternative prior art processes whichemploy dry-developable release layer concepts. In each process thephotoresist layer is wet-developed, while the release layer isdry-developed with separate plasma etching equipment. Additionally, thephotoresist layer, if hardened, must be lifted with harsh stripperswhich are either toxic and have disposal problems, or would bedeleterious to the substrate if the photoresist were removedsimultaneously with the release layer.

FIG. 1A-1F illustrates the six principle steps of the IBM Metal LiftoffProcess using dry-processable release layers.

FIG. 2A-2F illustrates the six principle steps of a tri-level processusing dry-developable planarizing layers (or very thick release layers).

FIG. 3A-3E illustrates the five principle steps of the IBM Ion MillingProcess for metal inter layers using dry-developable release layersystems.

FIG. 4A-4G illustrates the seven principle steps of themetal-over-release layer ion planarization mask process.

FIG. 5A-5D illustrates the four principle steps of the imaging processfor concurrently wet-developing the release layer and its adjacentpositive-working photoresist.

FIG. 6A-6F illustrates a prior art process for application of prior artpolyimide coatings starting with a polyamic acid solution, but whichpolyimide coatings can not be used as release layers for thephotoresist.

FIG. 7 illustrates a diagram of the polyamic acid chemistry involved inthe general manufacturer of such materials.

FIG. 8A-8E illustrates the process of the present invention usingwet-developable release layers to assist the removal of high-temperaturebaked photoresist.

FIG. 9A-9D illustrates ion implantation processes using thewet-developable release layer process of the present invention.

FIG. 10A-10D illustrates metal liftoff processes using thewet-developable release layer compositions of the present invention.

FIG. 11A-11D illustrates processes using the wet-developable releaselayers of the present invention as a planarizing film.

FIG. 12A-12B illustrates processes using the wet-developable film of thepresent invention to remove an epoxy encapsulant.

FIG. 13 illustrates the formulas of a+b two polyimide resins useful asrelease layers in the present invention.

DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS

The release layer compositions of the present invention are generallyderived from the polyamic acid chemistry depicted at FIG. 7 but withcritical differences from past polyamic acid/imides.

In the past, such polyimide coatings have been generally offered for usein microlithographic processes because they have good chemicalresistance, high temperature stability, and good dielectric properties.They have been used as one of a few organic materials which can replaceglass dielectrics and passivation coatings in IC devices. In FIG. 7, theletter R equals --CH₂ --, --O--, --S--, ##STR1## and other bridginggroups and the letter n represents the number of repeat units in thepolymer and is usually greater than 10.

These compositions are not normally spin-coated directly from solution ithe polyimide form. Instead they are applied by spin-coating in theprecursor polyamic acid form. The polyamic acid precursor then is heatedto approximately 170 degrees C to remove the solvents and to partiallyimidize the film. This allows a controllable etch rate in alkalinedevelopers as the composition is then patterned along with a photoresistlayer. After patterning and stripping the resist, the polyamic acid filmis heated to above 200 degrees C to complete the imidization and remainson the substrate.

There is a strong inverse relationship between temperature andsolubility which renders these prior art polyamic acids of little use inrelease layer technology. That is, prolonged exposure to temperaturesabove 150 degrees C and substantial imidization reduce the level ofsolubility in alkaline media to the point that such polyamic acid/imideswould normally be of little use as a release layer.

Nevertheless, in accordance with the present invention it has beendiscovered that polyamic acid/imide compositions, in which acidicfunctional groups are interposed at regular positions alone polymerbackbone, will impart sufficient solubility in alkaline media to convertthese materials into useful release layers even after substantialimidization. This occurs with no deleterious effects on theco-development rate of small feature size patterns in the preferredembodiments of the present invention.

The acidic functional groups may include, for example, carboxylic acids(--COOH), aromatic hydroxyls (aryl-OH), and sulfonic acid (--SO₃ H).Typical acid functionalized polymers may be seen at FIG. 13A and FIG.13B. It is particularly preferred that the acidic functional moieties beattached to the diamine side of the polyamic acid/imide because it issynthetically more convenient to prepare the functionalized diaminesthan to prepare functionalized dyanhydrides.

It is important to know that the polyamic acid/imides of the presentinvention remain sufficiently soluble inspite of the high thermalimidization which would otherwise render prior art polyamic acid/imidesunsuitable as release layers.

Diamines with acidic functionalities suitable in condensation reactionsfor preparing compositions of the present invention are commerciallyavailable. Among the preferred group of such diamines is as follows:

3,5-diaminobenzoic acid (and other isomers such as the 3,4-isomer),

3,3'-dihydroxy-4,4'-diaminobiphenyl,

o-tolidine disulfonic acid,

2,4-diaminophenol,

3-amino-4-hydroxyphenyl sulfone,

3,3'-dicarboxy-4,4'-diaminobiphenyl,

2,4-diamino-6-hydroxypyrimidine,

2,5-diaminobenzensulfonic acid,

Many dianhydrides can be used to react with the functionalized diamines.Suitable dianhydrides include the following:

3,3'4,4'-benzophenone tetracarboxylic dianhydride (BTDA) pyromelliticdianhydride (PMDA)

3,3', 4,4'-biphenyl tetracarboxylic dianhydride (BPDA) diphenylsulfone-3,3',4,4'-tetracarboxylic dianhydride.

Two especially preferred release layer compositions, shown in FIGS. 13aand 13b, are copolymers of 3,5-diaminobenzoic acid and BTDA and3,3'-dihdyroxy-4,4'-diaminobiphenyl and PMDA.

Materials resembling the hydroxy polyimide shown in FIG 13b wererecently reported by Khanna and Mueler (10) as being suitable bases forhigh temperature-stable positive photoresists. These materials werebased on diamines and dianhydrides with fluorinated bridging groups.They are unsuitable for purposes of the present invention because theyare soluble in photoresist solvents and can be removed when the resistis spincoated. Moreover, they are extremely expensive.

Only a few combinations of the above diamines and dianhydrides arespincoatable in the form of polyimides. Accordingly, it is particularlypreferred in the process of this invention to spincoat the materials aspolyamic acids and then thermally cure them to the polyimide form beforedevelopment.

Preferred solvent systems for polyamic acid preparation and spincoatinginclude alkyl amides such as N-methylpyrrolidone and dimethylacetamide,methyl sulfoxide, cyclic ketones such as cyclohexanone, and glymes suchas 2-methoxyethyl ether.

The development rate of the polyimide release films in aqueous base ishighly dependent on the polymer structure. Generally speaking, thegreater the level of acidic functional moieties on the polyimide, thefaster the development rate. Some monomer combinations yield polyimideswhich develop too fast at desired bake temperature and cannot bepatterned to small feature sizes, for example, 3,5 diaminobenzoic acidand PMDA rather than BTDA baked for 30 minutes at 200 C rather thanBTDA. In such instance it is preferred that the development rate bereduced by including other diamine components which do not bear acidicfunctional groups into the polymer structure. High molecular weightaromatic diamines are particularly useful in this regard since they havea large dilution effect on the polymer repeat unit. A large number ofsuch diamine materials have been described in the literature, forexample, see the general reference "Polyimides: Synthesis,Characterization, and Applications," Vols. I & II; K. L. Mittal, Ed.;Plenum Press, New York (1984). A few preferred diamines are

4,4'-oxydiamiline, or ODA, (particularly when copolymerized with PMDA),

2,2-bis [4-(4-aminophenoxy)phenyl propane, or BAPP,bis[4-(4-aminophenoxy)ophenyl]sulfone, or BAPPS.

One particularly preferred embodiment of this invention comprisesterpolymers of 3,5-diamiobenzoic acid/BTDA/BAPPS wherein the mole ratiof 3,5-diaminobenzoic acid to BAPPS is 2:1 to 4:1.

Another way to slow the development rate of the release layer films, butwithout resorting to strucutural modifications, is through the use ofadditives. These include compatible polymers with low developersolubility and reactive-low-molecular weight (MW) compounds which arecapable of crosslinking the release layer polymer.

Multinational epoxides compounds are especially effective, low MWadditives. In a preferred embodiment of the invention it is notnecessary to completely imidize (to more than 50%) release films beforethey are developed when these additives are present. Unlike other usesof these additives, the extra acidity contributed by an uncyclized amicacids is apparently compensated for by the additive. A related benefitof additive use is that the curing temperature of the film can bereduced. Traditional bisphenol A-type epoxy resins and cycloaliphaticdiepoxides are effective additives when used at 1-20 wt. % based onpolyamic acid solids.

An alternative means for reducing the imidization requirements is tomodify the polymer by esterifying acid positions of the amic acid groupwith either an aromatic or aliphatic alcohol. This causes essentiallythe same change in solubility as imidization. If esterification isemployed, the bake requirements may be reduced to as low as 100 C. Otherrelease layer properties such as high temperature stability andsolubility in alkaline media are unaffected.

In accordance with the preferred method of this invention the polyamicacids are prepared as follows: The diamine (s) is (are) charged into asealable reactor fitted with a heavy stirrer and nitrogen purge. It isdissolved in a portion of the solvent. The dynahydride is then washedinto the stirring diamine solution with the balance of the solvent togive a dianhydride/diamine mole ratio in the range 0.700-1.100. Ratiosin the range 0.85-1.00 are preferred. The solution is allowed to stir atambient temperature for 24 hours to complete the polymerization. Thepolymer solids level is usually adjusted to 10-25 wt. %.

The polyamic acid solution is diluted to any convenient level needed toobtain a desired film thickness when spincoated. Additives, ifnecessary, should be dissolved in the polyamic acid solution usingvigorous mixing. After formulation, the products are preferrably storedunder refrigerated conditions to preserve physical and chemicalproperties. Thereafter, they may be distributed and employed as releaselayers in microlithographic imaging processes.

The basic imaging process for the polyimide release layer compositionsis described in FIG. 5. The processes described in FIGS. 8-11 arestandard schemes which may use release layer composition of the presentinvention. The unique properties of base-soluble polyimides also makesthem applicable to these, device-related processes where intractablelayers must be removed. These processes may or may not entailphotoimaging.

The release layer materials are useful on all semiconductor substratesincluding silicon, silicon dioxide, silicon nitride, silicon carbide,glasses, gallium arsenide, aluminum and other metals. Application of anadhesion promoter, such as hexamethyldisilazane or anorganotrialkoxysilane, to the substrate before coating the release filmdoes not deteriorate performance and may be employed if desired forcertain types of lithographic quality.

After spincoating, the release film is preferrably baked to cause morethan 80% imidazation of the film unless esterified polymers or low MWadditives are used. Preferred bake temperatures lie in the range140°-250° C. The most preferred temperature (which provides the bestlithographic control), is obtained by correlating the structure of therelease polymer and the type of solvents used for spincoating. Forexample, higher bake temperatures are required for thick films spun fromheavy solvents such as N-methyl-pyrrolidone.

Convection oven baking, infrared track, and hotplate baking giveacceptable results. Oven bake times range from 5-120 minutes; hotplatebake times range from 15-300 seconds. Where desired, imidization canalso be achieved by chemical techniques including exposure to gaseousreagents and high energy beams.

Application of the positive photoresist, softbaking, exposure anddevelopment may follow the procedures recommended by the manufacturer ofthe photoresist.

The preferred developers are aqueous solutions of sodium or potassiumhydroxides, tetramethylammonium hydroxide, choline hydroxide, and otheraqueous alkalies. During the development step, the photoresist is etchedaway first, exposing the release layer film, which is developedconcurrently although second in sequence. The time required to developthe release layer film will depend on its thickness, its thermal historyand its structure. Preferably 5 to 120 seconds is sufficient.Overdevelopment is preferrably avoided because it will continue toundercut beneath the resist (FIG. 5). In liftoff processes (FIG. 10),however, a certain degree of undercut is preferred.

A variety of processing steps may occur before the photoresist is lifted(by dissolving the release layer). These include substrate etching bywet or dry methods, metal deposition, glass deposition ion implantationand various high temperature processes. The good chemical resistance andexcellent high temperature stability of polyimide release films meansthat they will pass through these steps largely unaffected.

Release of the resist is accomplished by immersing or spraying thespecimen wit an alkaline solution that dissolves the release layercomponent. A room temperature photoresist developer or heated developercomprising aqueous alkali can often serve as the release bath.Sometimes, at higher processing temperatures, flowed resist may coverthe exposed edges of the release layer pattern and impede thepenetration of the aqueous alkali release bath into the release layer.

In these instances, it is preferred to add to such a release bath anorganic solvent to assist penetration such as glycol ether and/orN-methyl-pyrrolidone. In a particularly preferred embodiment anonaqueous alkaline media is employed comprising organics such as glycolethers or N-methylpyrrolidone with the nonaqueous alkali ethanolamine.This nonaqueous alkaline component, such as ethanolamine, can beparticularly effective to cause dissolution of the polyimide releasefilms where simple organic solvent mixtures are not effective alone. Theimmersion or spray time required to lift the resist varies with theprocessing conditions. Complete resist removal generally occurs within1-60 minutes under immersion conditions.

The processes of the invention have been described with the use ofpositive photoresists because of their preferred use in themicroelectronics industry and the codevelopment objective. In principal,the polyimide release layer materials of this invention can be equallyapplicable to processes involving electron beam, x-ray, negative anddeep UV resists.

These imaging systems, however, require an organic solvent mixture asthe developer rather than aqueous alkali. Since polyimide release filmsare highly resistant to organic solvents, this does not present aproblem, but a two-step development procedure would be needed; firstusing an organic solvent to develop the resist, then the release layerwould be developed using aqueous base.

GLOSSARY OF TERNS

1. positive photoresist--Usually a mixture of an alkali-soluble phenolicresin (novolac) and a photosensitive dissolution inhibitor. In thisform, the mixture cannot be dissolved in aqueous alkali to produce animage. Exposure of the resist to UV light causes the photoinhibitor tochemically rearrange forming a carboxylic acid compound. This compoundand the phenolic resin can then be etched away by aqueous base (ordeveloper) to create a positive image. Hence, the term"positive-working" resist.

2. planarization--The ability of a polymer coating to create a levelsurface when spincoated over irregular topography.

3. strippers--Liquid chemical media used to remove photoresists afterprocessing is finished. Strippers are normally of two types: 1) mixturesof strong aqueous acids or bases with hydrogen peroxide, and 2) organicsolvent mixtures which may contain organic bases to speed attack onpositive photoresist.

4. developers--For positive resists, generally 1-10% aqueous solution ofan alkali metal hydroxide or a tetraalkylammnoium hydroxide. Thesolutions may also contain buffers and surfactants.

wet-developed or wet-processed--Refers to an etching process wherein anaqueous developer is used to pattern a photoresist or release layerfilm.

6. wet-etching--Any etching process for resist, glass, silicon, etc.,which involves a liquid etchant.

7. dry-developed or dry-processed--Refers to an etching process whereinan aqueous developer is used to pattern a photoresist or release layerfilm or other layer within a masking structure.

8. dry-etching--Any process for resist, glass, silicon, etc., which usesreactive ions as the active etching species.

9. plasma-developed or plasma-processed--Same as 7, but ion source isnondirectional, i.e. it etches isotropically.

10. reactive ion etching on (RIE)--Same as 8, but ion stream is focussedso that it etches only in the direction of focus.

11. Ion implantation--The use of a high energy ion beam to introducedopant atoms into semiconductor substrates.

12. ion milling--Similar to 10, but the ion species is concentrated intoa high energy beam.

13. glasses and dielectrics--Electrically insulating inorganic coatingssuch as silicone dioxide, silicon carbide, and silicone nitride.Sometimes used as a mask for dry-processing of underlying organic filmsby oxygen plasma or oxygen RIE. Glasses may be grown at hightemperature, e.g silicon dioxide coatings at about 1000° C. in thepresence of water vapor. They may also be produced by chemical vapordeposition (CVD) which involves the introduction of reactive gases overa substrate at high temperatures. Still another technique is theapplication of spin-on-glass coatings (SOG's ). SOG's are solutions oforganosilicon compounds which form loosely structured glasses whenheated at high temperatures.

14. sputtering--A coating process wherein collision of a ionized gaswith a metal target causes metal atoms to be transferred from the targetonto a substrate.

The following examples and tables are illustrative of the invention.

EXAMPLE 1

A variety of wet-developable polyimide release layers we re prepared anddemonstrated using the following procedures: The materials shown inTable 1 were applied in their polyamic acid form onto these three inchsilicon or silicon dioxide wafer substrates by spincoating. Solutionsolids were adjusted to approximately 6 wt. % to give a 2000-2500A filmwhen spin at 4000 RPM for 60 seconds. The films were then imidized bybaking. Bake temperatures wer correlated to provide the best lithographyat 1-2 micron feature sizes. Positive photoresists (SHIPLEY MICROPOSIT1470) were spun over the release films at 5000 RPM for 30 seconds andthen softbaked at 110° C. for 15 minutes on an infrared track. Finalresist thicknesses were about 1 micron. The wafers were developed in aroom temperature solution of 1:1 (v/v) SHIPLEY Microposit-MF-312 anddeionized water. (MF-312 is a concentrated aqueous solution oftetramethylammonium hydroxide and buffers.) Development time rangedbetween 5 and 15 seconds to give good quality 2.0 micron geometriesconcurrently in both the resist and the release layers. The ability tolift the resist after high temperature baking of the releaselayer-resist composite was used to test release capability. The testspecimens were baked at 200° C. for 30 minutes in a convection ovenafter development. This treatment rendered the resist virtuallyinsoluble in conventional commercial organic strippers, organic solvents(excluding hot phenols), and aqueous-base developers.

Control wafers with photoresist coated directly over the substrate (norelease film was present) showed less than 5% pattern removal within 15minutes when placed in the release baths. Although the control test arenot shown in Table 1 each control used unidentical release bath to itsrespective release sample. With the release film present, however, morethan 90% of the pattern could be lifted within 15 minutes. Two releasebaths were tested. The first [BATH 1] warm developer (60° C.); thesecond [BATH 2] was a 60/20./20 (v/v/v) mixture of dipropylene glycolmethyl ether, N-methylpyrrolidone and ethanolamine heated to 65° C.

Table 1 gives the composition of the release materials and otherpertinent conditions which provided the lithographic quality and releaseresults indicated.

                                      TABLE 1                                     __________________________________________________________________________                               Additive            Release                           Substrate                                                                          Monomers/Moles                                                                           Solvent Conditions                                                                             Imidization Conditions                                                                   Bath  Results                  __________________________________________________________________________    (1)                                                                              Silicon                                                                            3,5 diamino-                                                                             N-methyl                                                                              none     210° C. for                                                                       2     Greater than 90%                 benzoic/1.0                                                                              pyrrolidone      30 Minutes       release in 5                     BTDA/1.0   and diglyme      in oven          minutes                  (2)                                                                              Silicon                                                                            3,5 diamino-                                                                             N-methyl                                                                              none     210° C. for                                                                       2     Greater than 90%            Dioxide                                                                            benzoic/1.0                                                                              pyrrolidone      30 Minutes       release in 5                     BTDA/1.0   and diglyme      in oven          minutes                  (9)                                                                              Silicon                                                                            3,5 diamino-                                                                             N-methyl                                                                              Cycloaliphatic                                                                         195° C. for 30                                                                    2     Greater than 90%                 benzoic/1.0                                                                              pyrrolidone                                                                           diepoxide                                                                              minutes in oven  release in 5                     BTDA/1.0   and diglyme                                                                           (Cyracure 6100)           minutes                                             by Union Carbide                                                              10 Wt. % of                                                                   nomer solids                                       (3)                                                                              Silicon                                                                            3,5 diamino-                                                                             N-methyl                                                                              none     210° C. for                                                                       1     Greater than 90%                 benzoic/1.0                                                                              pyrrolidone      30 minutes in oven                                                                             release in 5                     BTDA/1.0   and diglyme                       minutes                  (4)                                                                              Silicon                                                                            3,5 diamino-                                                                             N-methyl                                                                              none     190°  C. for 30                                                                   2inutes                                                                             Greater than 90%                 benzoic/0.75                                                                             pyrrolidone      in oven          release in 5                     BAPP/0.25  and diglyme                       minutes                          BTDA/1.0                                                              (5)                                                                              Silicon                                                                            3,5 diamino-                                                                             N-methyl                                                                              none     195° C. for 2                                                                     2inutes                                                                             Greater than 90%                 benzoic/0.75                                                                             pyrrolidone      on hotplate      resist release in                BAPP/0.25  and diglyme                       5 minutes                        BTDA/1.0                                                              (6)                                                                              Silicon                                                                            3,5 diamino-                                                                             N-methyl                                                                              none     190° C. for 30                                                                    1inutes                                                                             Greater than 90%                 benzoic/0.75                                                                             pyrrolidone      in oven          resist release in                BAPP/0.25  and diglyme                       5 minutes                        BTDA/1.0                                                              (7)     3,5 diamino-                                                                             N-methyl                                                                              none     200° C. for 30                                                                    2inutes                                                                             Greater than 90%                 benzoic/0.75                                                                             pyrrolidone      in oven          resist release in                BAPPS/0.25 and diglyme                       5 minutes                        BTDA/1.0                                                              (8)                                                                              Silicon                                                                            3,5 diamino-                                                                             N-methyl                                                                              none     200° C. for 30                                                                    2inutes                                                                             Greater than 90%                 benzoic/0.75                                                                             pyrrolidone      in oven          resist release in                BAPPS/0.25 and diglyme                       5 minutes                        BTDA/1.0                                                              (10)                                                                             Silicon                                                                            Same as Sample 1                                                                         N-methyl                                                                              A epoxy resin                                                                          195° C. for 30                                                                    2inutes                                                                             Greater than 90%                            pyrrolidone                                                                           (Shell Epon 828)                                                                       in oven          resist release in                           and diglyme                                                                           10 wt. % of               5 minutes                                           monomer solids                                     (11)                                                                             Silicon                                                                            3,5 diamino-                                                                             N-methyl                                                                              Union Carbide                                                                          175° C. for 30                                                                    2inutes                                benzoic/0.75                                                                             pyrrolidone                                                                           Cyracure 6100                                                                          in oven                                           BAPPS/0.25 and diglyme                                                                           Cycloaliphatic                                             BTDA/1.0           diepoxide at                                                                  10 wt. % of                                                                   monomer solids                                     (12)    3,5 diamino-                                                                             N-methyl                                                                              Union Carbide                                                                          190° C. hotplate                                                                  2     90% release                      benzoic/0.75                                                                             pyrrolidone                                                                           Cyracure 6100                                                                          for 2 minutes                                     BAPPS/0.25 and diglyme                                                                           Cycloaliphatic                                             BTDA/1.0           diepoxide at                                                                  10 wt. % of                                                                   monomer solids                                     (13)                                                                             Silicon                                                                            3,5 diamino-                                                                             N-methyl                                                                              none     200° C. for                                                                       2     90% release                      benzoic/0.80                                                                             pyrrolidone      30 minutes                                        ODA/0.20   and cyclohexa-                                                     BTDA/1.0   none                                                       (14)                                                                             Silicon                                                                            3,5 diamino-                                                                             N-methyl-                                                                             none     50° C. for                                                                        2     90% release                      benzoic/1.0                                                                              pyrrolidone      30 minutes in oven                                BPDA/1.0   and cyclohexa-                                                                none                                                       (15)                                                                             Silicon                                                                            3,5 diamino-                                                                             N-methyl-                                                                             none     200° C. at 30                                                                     2inutes                                                                             90% release                      benzoic/0.75                                                                             pyrrolidone                                                        BAPPS/0.25 and cyclohexa-                                                     BPDA/1.0   none                                                       (16)    3,3' dihydroxy-4,4'-                                                                     N-methyl-                                                                             none     200° C. at 30                                                                     2inutes                                                                             90% release                      dianinobiphenyl/1.0                                                                      pyrrolidone                                                        PMDA/1.0   and cyclohexa-                                                                none                                                       (17)                                                                             Silicon                                                                            Same as sample 16 but                                                                    N-methyl-                                                                             none     200° C. at 30                                                                     2inutes                                                                             >90% release in                  BTDA instead                                                                             pyrrolidone                       10 minutes                       of PMDA    and cyclohexa-                                                                none                                                       (18)                                                                             Silicon                                                                            Same as    Same as Same as  Same as    70° C.                                                                       No resist removal                Sample 1   Sample 1                                                                              Sample 1 Sample 1   N-methyl                                                                            because no                                                              pyrrolidone                                                                         alkaline component                                                            was present              ADDED EXAMPLES                                                                  Same criteria and results as Example 7, but polymer prepared in 75/25         diglyme/cyclohexanone.                                                        Imidization conditions were 190° C./2 min. on hotplate.              20.                                                                             Same criteria and results as Example 7, but 1.0 mole PMDA used to make        polymer rather than BTDA.                                                     Same criteria and results as Example 7, but substrate was silicon             dioxide.                                                                      Same criteria and results as Example 7, but substrate was aluminum.           Same criteria and results as Example 7, but imidization conditions were       205° C./2 minutes on a hotplate.                                     __________________________________________________________________________

We claim:
 1. A method for making a wet-developable, polyamic acid/imidemicrolithographic polymer lift-off coatings, having improved resistantto thermal insolubiliation in alkaline media comprising:(a) reacting, insuitable solvent to produce the polyamic acid,nonamic acidfunctionalized diamines, an effective amount of a suitable dianhydride,to interpose the acidic functional moieties at regular molar equivalentpositions along the polymer backbone; (b) coating the polyamic acid formonto a microelectric substrate as the lift-off coating; (c) thermallycuring the lift-off coating to render it insoluble in organic solventand to impart at least 80% imidization; (d) coating over the lift-offlayer with a positive photoresist dissolved in organic solvent; (e)photo imaging the overcoated photoresist and developing patterns in thelift-off coating concurrently after patterns are developed in thephotoresist with alkaline developer solution at feature sizes as smallas one micron,whereby the unexposed lift-off coating remains soluble inalkaline media even after being highly imidized.
 2. The method of claim1 wherein the reaction product of step (a) is esterified and imidizationis less than 50%.
 3. The method of claim 1 wherein the suitable reactionsolvent is selected from the group consisting of N-methylpyrolidone,dimethylacetamide, methyl sulfoxide, cyclohexanone, 2-methoxyethylether, and mixtures thereof.
 4. The method of claim 1 wherein thefunctionalized diamines are selected from the group consisting ofa)3,5-diaminobenzoic acid or it's 3,4isomer, b) 3,3'-dihdyroxy -4,4'-diaminobiphenyl, c) o-tolidine disulfonic acid, d) 2,4-diaminophenol, e) 3-amino -4- hydroxyphenyl sulfone, f) 3,3'-dicarboyx -4,4'- diaminobiphenyl, g) 2,4-diamino - 6-hydroxyprimidine, and h) 2,5-diaminobenzenesulfonic acid.
 5. The method of claim 1 wherein thedianhydrides are selected from the group consisting of:a) pyromelliticdianhydride b) 3,3',4,4'-benzophenone tetracarboxylic dianhydride; c)4,4'- (hexafluoroisopropylidene) - bis - (phthalic anhydride) d) 4,4'-oxydiphthalic anhydride, e) 3,3'4,4'-biphenyl tetracarboxylicdianhydride; f) diphenyl slfone - 3,3', 4,4'-tetracarboxylicdianhydride.
 6. The method of claim 1, wherein the diamine 3,5-diaminobenzoic acid is reacted with 3,3', 4,4'-benzphenonetetracarboxylic dianhydride.
 7. The method of claim 1 wherein thediamine is 3,3'-dihydroxy - 4,4'-diamine and the dianhydride ispyromellitic dianhydride.
 8. The method of claim 6 wherein the suitablereaction solvent is a mixture of N-methylpyrroldione and diglyme.
 9. Themethod of claim 1 wherein a substantial amount of the functionalizeddiamine is replaced with aromatic diamine which does not contain acidicfunctional moieties.
 10. The method of claim 9 wherein the aromaticdiamine is selected from the group consisting of 4,4'-oxydiamiline2,2-bis[4(4-aminophenoxy)phenyl]propane and bis[4-[4-aminophenoxy)phenyl] sulfone.
 11. The method of claim 10 wherein the reactionsproduct is the terpolymer b 3,5 -diaminobenzoic acid 3,3',4,4'-benzophenone tetracarboxylic dianhydride/bis [4-[4-aminophenoxy)phenyl] sulfone at a mole ratio f 3,5 -diaminobenzoic acid to BAPPS of2:1 to 4:1.
 12. The method of claim 1 further comprising addingmultifunctional epoxy resins or other polymers to slow the developmentrate without resorting to structural modification.
 13. The method ofclaim 12 wherein the epoxy resins are either bisphenol A-type epoxyresins or cycloaliphatic diexpoxides in amount of from about 1 to 10% byweight of the polyamic acid/amide solids.
 14. The method of claim 12wherein the copolymer 4,4'-oxydiamiline pyromellitic dianhydride is usedto slow the development rate.
 15. The method of claim 1 wherein thecomposition is cured at from about 120° C. to about 250° C.
 16. Themethod of claim 1 wherein the suitable reaction solvent is selected fromthe group consisting of alkylamides, cyclic ketones, and glymes.